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4.   Add to a solution of urea a few drops of hydro chloric acid
and a solution of sodium nitrite.     Effervescence occurs and
nitrogen and carbon dioxide are evolved.
CO(NH2)2 + 2HO.NO = 2 No + CO2 = 3^2^'
5.   Heat a little urea with soda-lime.    Ammonia is   evolved.
See Appendix, p. 267.
Thiocarbamide (Thiourea),
Reynolds, Trans. C/iem. Soc., 1869, 22, r ; Volhard, JT. $rakt.
Chem., 1874, (2), 9, 10.
50 grms. ammonium thiocyanate«
The ammonium thiocyanate is melted in a round flask in n
paraffin-bath, and kept at a temperature at which the mass re-
mains just liquid (140—145°) for 5—6 hours. The cooled melt is
powdered and ground with half its weight of cold water, which
dissolves unchanged ammonium thiocyanate, but little of the
thiourea. By dissolving* the residue in a little hot water, pure
thiourea is obtained, on cooling, in colourless, silky needles.
Yield 7—8 grams.
CNS.NH4 = CS(NH2)2.
Properties—Colourless, rhombic prisms (from dilute aqueous
solution), long silky needles (from concentrated solutions) ; m. p.
172°. Very slightly soluble in cold water (i part of thiourea dis-
solves in about n parts of water at the ordinary temperature).
Uric Acid, CO   C—NH
I        |[       >CO
Scheele (1776).
Uric acid is a product of the metabolism of trie animal
organism. It is usually prepared from guano, which is treated
first with dilute hydrochloric acid to remove phosphate of cal-
cium. The uric acid is then dissolved out with hot caustic soda
and the clear alkaline solution precipitated with acid.